Jaiswal A I, Dubey C, Swain S L, Croft M
Department of Biology, University of California San Diego 92093-0063, USA.
Int Immunol. 1996 Feb;8(2):275-85. doi: 10.1093/intimm/8.2.275.
We have investigated the roles of TCR and accessory co-stimulatory signals in the induction of CD40 ligand (CD40L) on CD4 cells. Using naive T cells form TCR transgenic mice, specific for a peptide of pigeon cytochrome c, we show that in contrast to IL-2 secretion, CD40L expression is regulated primarily by signalling through the TCR, is enhanced by accessory molecule interactions, but co-stimulatory signals play little if any role. CD40L was induced at high levels on naive T cells, peaking at 5 h, by class II MHC+ fibroblast antigen-presenting cells (APC) which expressed either ICAM-1, B7-1 or both molecules, whereas only low levels were induced by fibroblasts which did not express any accessory molecules. Differences in intensity and duration of expression were seen following stimulation with ICAM- and B7-expressing APC, with the presence of ICAM resulting in greater and longer expression, although both molecules together were most efficient. The involvement of co-stimulatory signals delivered from accessory molecules was investigated in systems where there was no effect on TCR signalling from adhesive interactions. Anti-CD3, or antigen-pulsed APC lacking accessory molecules, were used to provide the TCR signal, with co-stimulus from either anti-CD28 or accessory molecule-expressing fibroblasts not presenting antigen. Anti-CD3 in the absence of co-stimuli induced high CD40L expression but no IL-2 production and provision of co-stimulatory signals, although inducing large quantities of IL-2, did not increase CD40L expression. In addition, low CD40L expression induced by antigen presented in the absence of accessory molecules was not enhanced by co-stimulation, although IL-2 was strongly up-regulated. These studies suggest that efficient expression of CD40L on naive CD4 cells does require accessory molecules on APC. However, the role of these molecules for CD40L induction, as opposed to IL-2 secretion, is not one of co-stimulation but one of adhesion, presumably allowing stronger or more prolonged signals to be generated through the TCR. The synergistic role of ICAM and B7 during naive CD4 activation was confirmed using dendritic cells as APC, with nearly complete inhibition of CD40L expression as well as IL-2 secretion being seen when both CTLA-4-Ig and anti-LFA-1 were used to block these molecules.
我们研究了T细胞受体（TCR）和辅助共刺激信号在诱导CD4细胞上的CD40配体（CD40L）中的作用。使用来自TCR转基因小鼠的初始T细胞，其对鸽细胞色素c的一种肽具有特异性，我们发现与白细胞介素-2（IL-2）分泌相反，CD40L的表达主要通过TCR信号传导来调节，通过辅助分子相互作用增强，但共刺激信号即使有作用也很小。在表达细胞间黏附分子-1（ICAM-1）、B7-1或两者的II类主要组织相容性复合体（MHC）+成纤维细胞抗原呈递细胞（APC）作用下，初始T细胞上的CD40L被高水平诱导，在5小时达到峰值，而不表达任何辅助分子的成纤维细胞仅诱导出低水平的CD40L。在用表达ICAM和B7的APC刺激后，观察到表达强度和持续时间的差异，ICAM的存在导致更高和更长时间的表达，尽管两者一起作用时最有效。在对黏附相互作用对TCR信号传导无影响的系统中，研究了辅助分子传递的共刺激信号的参与情况。使用抗CD3或缺乏辅助分子的抗原脉冲APC来提供TCR信号，同时来自抗CD28或表达辅助分子但不呈递抗原的成纤维细胞提供共刺激。在没有共刺激的情况下，抗CD3诱导高CD40L表达但不产生IL-2，而提供共刺激信号虽然诱导大量IL-2产生，但并未增加CD40L表达。此外，在没有辅助分子的情况下由抗原诱导的低水平CD40L表达不会因共刺激而增强，尽管IL-2被强烈上调。这些研究表明，初始CD4细胞上CD40L的有效表达确实需要APC上的辅助分子。然而，这些分子对CD40L诱导的作用，与IL-2分泌相反，不是共刺激作用，而是黏附作用，大概是允许通过TCR产生更强或更长时间的信号。使用树突状细胞作为APC证实了ICAM和B7在初始CD4细胞活化过程中的协同作用，当使用细胞毒性T淋巴细胞相关抗原4免疫球蛋白（CTLA-4-Ig）和抗淋巴细胞功能相关抗原-1（LFA-1）来阻断这些分子时，观察到CD40L表达以及IL-2分泌几乎完全受到抑制。
